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I have icons (in png format) with a resolution of about 500x500 pixels and want to use them in app development around size 30x30 pixels. But when I resize them, they become very aliased.

How can I resize them so they remain crisp, without aliasing or blur? I am using Windows 10. I have GIMP installed, and am happy to use any free software.

For example I have a heart iconOriginal Image

When I scale it down in the app (by setting the width and height programatically), it becomes aliased: Scaled Image

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  • not decrease, resize is the proper term. Decrease would be more specific to file size. But most likely for such a drastic resizing you'd have to redo them or you'll lose too much detail. – Luciano Sep 13 '19 at 11:27
  • On the other hand, what file format are these icons? What tools do you have available? Please edit your question to add more detail. – Luciano Sep 13 '19 at 11:30
  • I can't help but think that .svg would be a better file format. — There are some asset managers that can export files in different formats, colors and sizes. On Mac I use iconJar. That said, I get that this is probably not useful information for you in this case, but maybe in the future... – Joonas Sep 13 '19 at 12:29
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When using bitmap files like PNG, it is always better to have a specialised program handle sizing. Though browsers have been much improved in this regard throughout the years, they are not as heavily optimised as specialised image handling programs such as Photoshop or GIMP.

Photoshop has a batch image resizer, which you can find under File > Scripts > Image processor.

GIMP does not have a handy out-of-the-box tool, but has some options. If you're not afraid of scripting, you can use the Command Line Interface. There are also a few plugins that provide a Use Interface, such as BIMP or David's Batch Processor.

ImageMagick is a command line tool that can handle all kinds of image manipulation, including batch resizing. You can find a tutorial here.

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    I used ImageMagick. It made it a bit too blurry but I figured that scaling the image down partially and then programitically resizing found a nice middle ground. Thanks! – mahclark Sep 13 '19 at 22:26
  • Glad to hear it helped. – PieBie♦ Sep 14 '19 at 9:07

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